Abstract: The dialectic relationship between social capital and grassroots sport is addressed. Social capital theory guides the research of grassroots sport with a new conceptualization, explanatory mechanisms, innovative measurements, and a China-West comparative framework. Grassroots sport is an important field through which to develop social capital because spectators, participants, and volunteers in sporting activities are full of interpersonal and intergroup relationships, which produce and reproduce social capital at individual and collective levels. Therefore it is held that grassroots sports are to be developed and organized through neighborhood ties to improve the participation, and through community networks to create new management strategies, and through social media to establish and maintain sports fans community, finally through social capital strengths of the country to innovate the concept of grassroots sport development from the social capital perspective.Based on these theoretical discussions, an outline of concepts and measures of sport social capital are proposed in hopes of developing a public data archive on the sociology of sport in China.